This invention relates in general to apparatus for and a method of controlling the movement of a movable element of a machine, such as a boom of a mining machine, and more particularly to apparatus for and a method of controlling the downward or upward cut by a mining machine in a seam of material to be mined (coal, for example) overlying or underlying a stratum of undesired material (clay, for example) to reduce the quantity of undesired material mined with the desired material. It is especially concerned with apparatus for and a method of controlling the cutting by a continuous miner of the type generally comprising a carriage, a cutter boom mounted on the carriage for up-and-down movement relative to the carriage, and a cutter carried by the boom adapted to cut down into the seam of desired material on lowering the boom.
Heretofore, operators of mining machines and particularly machines of the type known as continuous miners, have used a variety of methods to determine when the machine is cutting or "shearing" beyond the limits of the seam of the desired material (coal, ore) and into the undesired bottom (or top) material (e.g., clay). Some operators, for example, have relied on their vision to alert them, a change in the color of the cuttings indicating that the miner is cutting beyond the seam of the desired material. Others have depended on their sense of touch, i.e., on their ability to "feel" a difference in the operation of the miner when it begins to cut into undesired material below or above the seam of the desired material, or on their sense of hearing to hear the difference. However, all these methods have proven to be unsatisfactory for confining the cut of the mining machine to the seam of the desired material. They generally result in an undue amount of undesired material (e.g., clay) being mined with the desired material (e.g., coal). This, in turn, has caused considerable waste of mining time and effort as well an increased costs for preparation (cleaning) of the desired material and waste disposal.
Moreover, the "vision" test is wholly ineffective after cutting or sumping into a coal seam (for example) a relatively short distance (10-20 feet) since all visual perceptions necessary for guiding the miner are lost after that distance. It has been necessary in the past for the mining machine (e.g., the continuous miner) constantly to be withdrawn from one place and moved to another (known as "tramming") while the one place is shored up, cleaned and otherwise prepared for further mining. The excessive amount of time spent in tramming due to the inability to make cuts of a greater distance has necessarily reduced the amount of time available for mining coal. Penetration deeper than 10-20 feet (e.g., 30-40 feet) into a seam is possible utilizing remote control of the mining machine, but in such mode of operation the operator is too far back from the machine to see, and, being off the machine, has no sense of touch as to the operation.